1. Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/04.0002
Anglicky v odborných předmětech "Support of teaching technical subjects in English“
Tutorial: Mechanic - electrician
Topic: Electronics
II. Class
Operational Amplifiers:
Comparators – Part 1 - Basics
Prepared by: Ing. Jaroslav Bernkopf
AVOP-ELEKTRO-Ber-010
Projekt Anglicky v odborných předmětech, CZ.1.07/1.3.09/
je spolufinancován Evropským sociálním fondem a státním rozpočtem České republiky.

2. Vi+ Vout Vi- A comparator is a device that compares two voltages.
Comparators – Part 1 - Basics
Definition
A comparator is a device that compares two voltages.
Its output indicates which of the input voltages is larger.
Vout
Vi+
Vi-
Operational Amplifiers

3. Comparators – Part 1 - Basics
Description
If the voltage on the non-inverting input (Vi+) is higher than the other voltage (Vi-), the output voltage Vout is positive.
And vice versa:
If Vi+ is lower than Vi-, the output voltage Vout is negative.
Vout
Vi+
Vi-
Operational Amplifiers

4. Vout Vout is positive, because Vi+ is higher than Vi-. Vi- Vi-
Comparators – Part 1 - Basics
Description
Vout
Vout
is positive, because
Vi+
is higher than Vi-.
Vi-
is higher than Vi+
therefore
Vout
is negative.
Vi-
Vi+
Operational Amplifiers

5. Operational amplifiers as comparators – disadvantages
Comparators – Part 1 - Basics
Description
Operational amplifiers as comparators – disadvantages
Operational amplifiers are slow.
Their output levels are not „logic“.
Operational Amplifiers

6. Operational amplifiers are slow.
Comparators – Part 1 - Basics
Description
Operational amplifiers are slow.
When a fast signal of a high frequency is applied to the inputs, an operational amplifier reacts too lazily.
It needs a long time to wake up and then another long time to transit from one level to the other.
Vout
Vi+
Vi-
Operational Amplifiers

7. Operational amplifiers are slow.
Comparators – Part 1 - Basics
Description
Operational amplifiers are slow.
The output Vout should start moving here
– when Vi+ becomes lower than Vi-.
But it starts more than 0.5μs later – here.
And stops moving another 2.5 μs later – here.
Vout
Vi+
Vi-
Operational Amplifiers

8. Output levels of operational amplifiers are not „logic“.
Comparators – Part 1 - Basics
Description
Output levels of operational amplifiers are not „logic“.
The high level output voltage should have a „TTL“ value, i.e. +5 V maximum. Here it is about V.
The low level output voltage should be near to zero. Here it is
about V.
Vout
Vi+
Vi-
Operational Amplifiers

9. Comparators – Part 1 - Basics
Task
Complete the picture below. Suppose the extreme output voltages are ±13.5 V.
Vi+
Vi-
Vout = ???
Operational Amplifiers

10. Vi+ Vi- Vout Solution Comparators – Part 1 - Basics
Operational Amplifiers

11. References Comparators – Part 1 - Basics http://www.wikipedia.com
Operational Amplifiers